KR102430190B1 - Integrated lnt-twc catalyst - Google Patents

Abstract

A layered catalyst composite for the treatment of exhaust gas emissions effective to provide lean NO _x trap functionality and three-way conversion functionality is described. The layered catalyst composite may include a catalytic material on a substrate, the catalytic material comprising at least two layers. The first layer comprises a rare earth oxide-high surface area refractory metal oxide particle, an alkaline earth metal supported on the rare earth oxide-high surface area refractory metal oxide particle, and at least one first platinum group supported on the rare earth oxide-high surface area refractory metal oxide particle. contains metal components. The second layer comprises a first oxygen storage component (OSC) and/or a second platinum group metal component supported on a first refractory metal oxide support, and optionally, a second refractory metal oxide support or a second oxygen storage component supported on the second oxygen storage component. and a third platinum group metal.

Description

Integrated LNT-TWC Catalyst {INTEGRATED LNT-TWC CATALYST}

The present invention relates to an exhaust gas purification catalyst and a method of using the same. More particularly, the present invention relates to a layered exhaust gas purification catalyst capable of performing both a NO _x absorption function and a three-way conversion (TWC) function, and this composite may be referred to as LNT-TWC. Exhaust gas purification catalysts can be used to treat exhaust gas streams, particularly those from lean burn engines.

Emissions of nitrogen oxides (NO _x ) from lean burn engines must be reduced to meet emission control standards. Conventional three-way conversion (TWC) automotive catalysts are suitable for the reduction of NO _x , carbon monoxide (CO) and hydrocarbon (HC) pollutants in engine exhaust operating at or near stoichiometric air/fuel conditions. The exact ratio of air to fuel that results in the stoichiometric condition depends on the relative ratios of carbon and hydrogen in the fuel. An air-to-fuel (A/F) ratio of 14.65:1 (weight of air to weight of fuel) is a stoichiometric ratio corresponding to the combustion of hydrocarbon fuels having the average formula CH _1.88 , such as gasoline. Thus, the symbol λ is used to denote the result of dividing a particular A/F ratio by the stoichiometric A/F ratio for a given fuel, such that λ=1 is a stoichiometric mixture, λ>1 is a fuel-lean mixture, λ<1 is a fuel-rich mixture.

Engines to be used for passenger cars and the like, especially gasoline-fueled engines, are being designed to operate under lean conditions as a measure of fuel economy. Such future engines are referred to as "lean burn engines". That is, the air-to-fuel ratio in the combustion mixture supplied to such an engine remains significantly above the stoichiometric ratio, so that the exhaust gas produced is "lean", ie the oxygen content of the exhaust gas is relatively high. Although lean burn engines provide advanced fuel economy, they have the disadvantage that conventional TWC catalysts are not effective in reducing NO _x emissions from such engines due to the excess oxygen in the exhaust. Attempts to overcome this problem have included the use of NO _x traps. The exhaust of such engines is treated with a catalyst/NO _x adsorbent that stores NO _x during lean (oxygen-rich) periods of operation and releases the stored NO _x during periods of rich (fuel-rich) operation. During the rich (or stoichiometric) period of operation, the catalytic component of the catalyst/NO _x adsorbent is formed by the reaction of NO _x (including NO _x released from the NO _x adsorbent) with HC, CO, and/or hydrogen present in the exhaust. It promotes the reduction of NO _x to nitrogen.

In a reducing environment, lean NO _x traps (LNTs) promote the steam reforming reaction and water gas shift (WGS) reaction of hydrocarbons to activate the reaction by providing H ₂ as a reducing agent to reduce NO _x . A water gas shift reaction is a chemical reaction in which carbon monoxide reacts with water vapor to form carbon dioxide and hydrogen. The presence of ceria in the LNT catalyzes the WGS reaction, improving the resistance of the LNT to SO ₂ inactivation and stabilizing the PGM. Alkaline earth metal oxides such as oxides of Mg, Ca, Sr, and Ba, alkali metal oxides such as oxides of Li, Na, K, Rb, and Cs, and rare earths in combination with noble metal catalysts such as platinum dispersed on an alumina support NO _x storage (adsorbent) components comprising metal oxides such as oxides of Ce, La, Pr, and Nd have been used to purify exhaust gases from internal combustion engines. For NO _x storage, baria is typically preferred because it forms nitrates in lean engine operation and releases nitrates relatively easily under rich conditions. However, catalysts using baria for NO _x storage present problems in practical applications, especially when the catalyst is aged by exposure to high temperature and lean operating conditions. After such exposure, such catalysts have markedly reduced catalytic activity for NO _x reduction, especially at low temperature (200-350° C.) and high temperature (450° C.-600° C.) operating conditions. NO _x storage materials comprising barium (BaCO ₃ ) immobilized on ceria (CeO ₂ ) have been reported, and these NO _x materials exhibited improved thermal aging properties.

To meet current government regulations (eg Euro 6), catalytic converters must effectively convert hydrocarbons at low temperatures during lean operation, and also convert hydrocarbons and NO _x under conditions favorable to stoichiometric exhaust gases. should be effectively converted. A further challenge is to store nitrogen oxides during lean operation and reduce these oxides during rich operation. However, due to space constraints, the use of stand-alone TWCs with stand-alone LNT catalysts is not ideal. Therefore, there is a need for a technique that balances standard TWC behavior and LNT functionality while solving the space problem that arises when a stand-alone TWC catalyst is used with a stand-alone LNT catalyst.

A first embodiment relates to a layered catalyst composite for an exhaust stream of an internal combustion engine, the layered catalyst composite comprising a catalytic material on a substrate, the catalytic material comprising at least two layers, wherein the first layer comprises: a rare earth oxide-high surface area refractory metal oxide particle, an alkaline earth metal supported on the rare earth oxide-high surface area refractory metal oxide particle, and at least one first platinum group metal component supported on the rare earth oxide-high surface area refractory metal oxide particle. do; The second layer comprises a first oxygen storage component (OSC) and/or a second platinum group metal component supported on a first refractory metal oxide support, and optionally, a second refractory metal oxide support or a second oxygen storage component supported on the second oxygen storage component. and a third platinum group metal.

In a second embodiment, the layered catalyst composite of the first embodiment is modified, wherein the catalyst is effective to provide both lean NO _x trap functionality and three-way conversion functionality.

In a third embodiment, the layered catalyst composite of the first and second embodiments is modified, wherein the first layer is disposed on a substrate comprising a flow-through monolith and the second layer is the first placed on the floor.

In a fourth embodiment, the layered catalyst composite of the first and second embodiments is modified, wherein the second layer is disposed on a substrate comprising a flow-through monolith and the first layer is disposed on the second layer.

In a fifth embodiment, the layered catalyst composite of the first to fourth embodiments is modified, wherein the substrate comprises a wall-flow filter, wherein the first layer is on the inlet set side of the passageway and the second layer comprises: It's on the exit set side of the aisle.

In a sixth embodiment, the layered catalyst composite of the first to fourth embodiments is modified, wherein the substrate comprises a wall-flow filter, wherein the first layer is on the side of the outlet set of passageways and the second layer is on the side of the inlet set of passageways. have.

In a seventh embodiment, the layered catalyst composite of the first to sixth embodiments is modified, wherein the layered catalyst composite is free of hydrocarbon trapping material.

In an eighth embodiment, the layered catalyst composite of the first to seventh embodiments is modified, wherein the rare earth oxide-high surface area refractory metal oxide particles are in the range of from about 20% to about 80% on an oxide basis by weight percent of the particles. It has an existing ceria phase.

In a ninth embodiment, the layered catalyst composite of the first to eighth embodiments is modified, wherein the rare earth oxide-high surface area refractory metal oxide particles comprise ceria-alumina particles.

In a tenth embodiment, the layered catalyst composite of the first to ninth embodiments is modified, wherein the ceria-alumina particles have a ceria phase present in the range of from about 20% to about 80% on an oxide basis by weight percent of the particles. have

In an eleventh embodiment, the layered catalyst composite of the first to tenth embodiments is modified, wherein the ceria-alumina particles are substantially free of alkaline earth metals.

In a twelfth embodiment, the layered catalyst composite of the first to eleventh embodiments is modified, wherein the first, second, and third platinum group metal components independently comprise platinum, palladium, and/or rhodium.

In a thirteenth embodiment, the layered catalyst composite of the first to twelfth embodiments is modified, wherein the first platinum group metal component comprises both palladium and platinum.

In a fourteenth embodiment, the layered catalyst composite of the first to thirteenth embodiments is modified, wherein the first platinum group metal component comprises platinum.

In a fifteenth embodiment, the layered catalyst composite of the first to fourteenth embodiments is modified, wherein the second platinum group metal component comprises palladium.

In a sixteenth embodiment, the layered catalyst composite of the first to fifteenth embodiments is modified, wherein the third platinum group metal component comprises rhodium.

In a seventeenth embodiment, the layered catalyst composite of the first to sixteenth embodiments is modified, wherein the first and second refractory metal oxide supports are independently alumina, zirconia, alumina-zirconia, lanthana-alumina, lanthana-zirconia- activated, stabilized, selected from the group consisting of alumina, baria-alumina, baria-lantana-alumina, baria-lanthana-neodymia-alumina, alumina-chromia, alumina-ceria, and combinations thereof or both include the corresponding compound.

In an eighteenth embodiment, the layered catalyst composite of the first to seventeenth embodiments is modified, wherein the first and second oxygen storage components comprise a ceria-zirconia composite or a rare earth-stabilized ceria-zirconia.

In a nineteenth embodiment, the layered catalyst composite of the first to eighteenth embodiments is modified, wherein the first oxygen storage component and the second oxygen storage component comprise different ceria-zirconia composites, and wherein the first oxygen storage component is 35 and wherein the second oxygen storage component comprises ceria in the range of from 15 to 25 weight percent and zirconia in the range of 70 to 80 weight percent and ceria in the range of from 45 to 45 weight percent and zirconia in the range of 43 to 53 weight percent.

In a twentieth embodiment, the layered catalyst composite of the first to nineteenth embodiments is modified, wherein the alkaline earth metal comprises barium.

In a twenty-first embodiment, the layered catalyst composite of the first to twentieth embodiments is modified, wherein barium is present in an amount ranging from about 5% to 30% by weight of the first layer on an oxide basis.

In a twenty-second embodiment, the layered catalyst composite of the first to twenty-first embodiments is modified, wherein the second layer further comprises a second alkaline earth metal supported on the first refractory metal oxide support.

In a twenty-third embodiment, the layered catalyst composite of the twenty-second embodiment is modified, wherein the second alkaline earth metal comprises barium.

In a twenty-fourth embodiment, the layered catalyst composite of the twenty-third embodiment is modified, wherein barium is present in an amount ranging from about 0% to about 10% by weight of the second layer on an oxide basis.

In a twenty-fifth embodiment, the layered catalyst composite of the first to twenty-fourth embodiments is modified, wherein under lean conditions, the layered catalyst composite is effective to simultaneously store NO _x and also oxidize CO, HC, and NO to NO ₂ to be.

In a twenty-sixth embodiment, the layered catalyst composite of the first to the twenty-fifth embodiments is modified, wherein under rich conditions, the layered catalyst composite is effective at simultaneously converting CO and HC and also releasing and reducing NO _x .

In a twenty-seventh embodiment, the layered catalyst composite of the first to twenty-sixth embodiments is modified, wherein, under stoichiometric conditions, the layered catalyst composite is effective to simultaneously convert CO, HC, and NO _x .

In a twenty-eighth embodiment, the layered catalyst composite of the first embodiment is modified, wherein the catalyst composite is effective to provide both lean NO _x trap functionality and three-way conversion functionality; the substrate comprises a flow-through carrier and the first layer is disposed on the substrate and the second layer is disposed on the first layer; wherein the rare earth oxide-high surface area refractory metal oxide particles comprise ceria-alumina particles having a ceria phase present in the range of from about 20% to about 80% on an oxide basis by weight percent in the composite; the first platinum group metal component comprises palladium and/or platinum; the second platinum group metal component comprises palladium; The third platinum group metal component includes rhodium.

A twenty-ninth embodiment relates to an exhaust gas treatment system comprising the layered catalyst composite of the first to twenty-eighth embodiments positioned downstream of an engine.

In a thirtieth embodiment, the exhaust gas treatment system of the twenty-ninth embodiment is modified, wherein the engine comprises a lean burn engine.

In a thirty-first embodiment, the exhaust gas treatment system of the thirtieth embodiment is modified, wherein the lean burn engine comprises a lean gasoline direct injection engine.

In a thirty-second embodiment, the exhaust gas treatment system of the twenty-ninth to thirty-first embodiments is modified to further comprise a catalyst selected from the group consisting of TWC, SCR, GPF, LNT, AMOx, SCR on filter, and combinations thereof. .

In a thirty-third embodiment, the exhaust gas treatment system of the twenty-ninth to thirty-second embodiments is modified to further include an SCR catalyst located downstream of the layered catalyst composite.

A thirty-fourth embodiment comprises contacting the gas with the layered catalyst composite of the first to twenty-seventh embodiments, wherein under lean conditions, the layered catalyst composite simultaneously stores NO _x and also oxidizes CO, HC, and NO. effective; Under abundant conditions, the layered catalyst complex is effective in simultaneously converting CO and HC and also releasing and reducing NO _x ; Under stoichiometric conditions, the layered catalyst composite is directed to a method of treating gases comprising hydrocarbons, carbon monoxide, and nitrogen oxides that are effective at simultaneously converting CO, HC, and NO _x .

A thirty-fifth embodiment comprises providing a carrier and coating the carrier with first and second layers of a catalytic material; the first layer is a rare earth oxide-high surface area refractory metal oxide particle, an alkaline earth metal supported on the rare earth oxide-high surface area refractory metal oxide particle, and at least one first platinum group supported on the rare earth oxide-high surface area refractory metal oxide particle A second platinum group metal component comprising a metal component and a second layer, which is the outermost layer of the composite, supported on a first oxygen storage component (OSC) or a first refractory metal oxide support and a second refractory metal oxide support or second oxygen It relates to a method for preparing a layered catalyst composite, comprising a third platinum group metal component supported on a storage component.

1 is a perspective view of a honeycomb type refractory substrate member that may include a layered catalyst composite according to an embodiment;
FIG. 2 is a partial cross-sectional view enlarged with respect to FIG. 1 and taken along a plane parallel to the end face of the substrate of FIG. 1, showing an enlarged view of one of the gas flow passages shown in FIG. 1;
3A is a graph of cyclic NO _x conversion according to Examples 1, 2, 3, 4, and 7 in the fresh state;
3B is a graph of NO _x trapping capacity according to Examples 1, 2, 3, 4, and 7 in the new state;
4A is a graph of cyclic NO _x conversion according to Examples 1, 2, 3, 4, and 7 after aging at 950° C. for 5 hours in 2% O ₂ in N ₂ and 10% water vapor;
4B is a graph of NO _x trapping capacity according to Examples 1, 2, 3, 4, and 7 after aging at 950° C. for 5 hours in 2% O ₂ and 10% water vapor in N ₂ ;
5A is a graph of aesthetic NO _x emissions according to Examples 1 and 4 after aging at 950° C. for 64 hours in an internal combustion engine;
5B is a graph of NMHC emissions according to Examples 1 and 4 after aging at 950° C. for 64 hours in an internal combustion engine;
6 is a TEM image of the undercoat of Example 1 in a new condition;
7 is a TEM image of the topcoat of Example 1 in a new state.

Before describing some exemplary embodiments of the present invention, it is to be understood that the present invention is not limited to the details of construction or process steps detailed in the description that follows. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

According to an embodiment of the present invention, there is provided a layered catalyst composite for an exhaust stream of an internal combustion engine that balances TWC action and LNT functionality. In lean operation, the catalyst complex allows conversion of carbon monoxide (CO) and hydrocarbons (HC) and storage of NO _x . In rich operation, the catalyst is effective in converting CO and HC and releasing and reducing NO _x . In stoichiometric operation, the catalyst complex allows for simultaneous conversion of CO, HC, and NO _x .

In one or more embodiments, the layered catalyst composite comprises a catalytic material on a substrate. The catalytic material comprises at least two layers, a first layer and a second layer. The first layer comprises a rare earth oxide-high surface area refractory metal oxide particle, an alkaline earth metal supported on the rare earth oxide-high surface area refractory metal oxide particle, and at least one first platinum group supported on the rare earth oxide-high surface area refractory metal oxide particle. contains metal components. The second layer comprises a first oxygen storage component (OSC) and/or a second platinum group metal component supported on a first refractory metal oxide support, and optionally, a second refractory metal oxide support or a second oxygen storage component supported on the second oxygen storage component. and a third platinum group metal.

With respect to terms used in this disclosure, the following definitions are provided.

As used herein, the term “catalyst” or “catalytic material” or “catalytic material” refers to a material that promotes a reaction. As used herein, the term “catalyst complex” refers to a carrier substrate having one or more washcoat layers containing a PGM component effective to catalyze the oxidation of a catalytic material, such as CO, HC, and NO, e.g. refers to a catalytic article comprising a honeycomb substrate.

As used herein, the terms “layer” and “lamellar” refer to structures supported on a surface, eg, a substrate. In one or more embodiments, the layered catalyst composites of the present invention are coated on a single substrate or substrate member, wherein one layer (eg, first or second layer) is coated on another layer (eg, second or second layer). It contains two distinct layers on top of the first floor). In one or more embodiments, the first layer is coated over the entire axial length of the substrate (eg, the flow-through monolith) and the second layer is coated over the entire axial length of the first layer. In another embodiment, the second layer is disposed on the substrate and the first layer is disposed on the second layer. In one or more embodiments, the first and second layers are washcoats.

As used herein, the term "washcoat" has its ordinary meaning in the art, which is a thin, adhesive coating of a catalytic or other material applied to a carrier base material, such as a honeycomb type carrier member, which is being treated It is sufficiently porous to allow passage of gas streams. As is understood in the art, a washcoat is obtained from a dispersion of particles as a slurry, wherein the dispersion is applied to a substrate, dried and then calcined to provide a porous washcoat.

As used herein, the terms "refractory metal oxide support" and "support" refer to an underlying high surface area material on which additional chemical compounds or elements are supported. The support particles have pores greater than 20 Angstroms and a broad pore distribution. Such metal oxide supports as defined herein exclude molecular sieves, specifically zeolites. In certain embodiments, the high surface area refractory metal oxide support typically exhibits, for example, a BET surface area greater than 60 square meters per gram (“m ² /g”), often up to about 200 m ² /g or greater,” Alumina support materials, also referred to as "gamma alumina" or "activated alumina", may be used. Such activated alumina is typically a mixture of alumina in gamma and delta phases, but may also contain significant amounts of eta, kappa, and theta alumina phases. A refractory metal oxide other than activated alumina may be used as a support for at least a portion of the catalytic component in a given catalyst. For example, bulk ceria, zirconia, alpha alumina, silica, titania, and other materials are known for such use.

One or more embodiments of the present invention are alumina, zirconia, alumina-zirconia, lantana-alumina, lantana-zirconia-alumina, baria-alumina, baria-lantana-alumina, baria-lantana-neodymia-alumina, alumina - a refractory metal oxide support comprising an active compound selected from the group consisting of chromia, ceria, alumina-ceria, and combinations thereof. Although many of these materials suffer from the disadvantage of having a significantly lower BET surface area than activated alumina, such disadvantages tend to be offset by increased durability or improved performance of the resulting catalyst. As used herein, the term “BET surface area” has its ordinary meaning to refer to the Brunauer, Emmett, Teller method for determining surface area by N ₂ adsorption. Pore diameter and pore volume can also be determined using a BET type of N ₂ adsorption or desorption experiment.

In one or more embodiments, the first and second refractory metal oxide supports are independently alumina, zirconia, alumina-zirconia, lanthana-alumina, lantana-zirconia-alumina, baria-alumina, baria-lantana-alumina, baria -lanthana-neodymia-alumina, alumina-chromia, ceria, alumina-ceria, and combinations thereof, activated, stabilized, or both. In a specific embodiment, the second refractory metal oxide comprises alumina.

As used herein, the term "space velocity" refers to the quotient of the incoming volumetric flow rate of reactants divided by the reactor volume (or catalyst bed volume), which indicates how many reactor volumes of feed can be processed per unit time. Space velocity is generally regarded as the reciprocal of reactor space time.

As used herein, the term “rare earth oxide-high surface area refractory metal oxide particles” refers to a mixture of rare earth oxide and high surface area refractory metal oxide particles used as a carrier for a catalytic component. In one or more embodiments, the rare earth oxide is selected from at least one oxide of a rare earth metal selected from Ce, Pr, Nd, Eu, Sm, Yb, and La, and mixtures thereof. In some embodiments, the rare earth oxide comprises one or more other components, such as lanthanum, praseodymium, neodymium, niobium, platinum, palladium, rhodium, iridium, osmium, ruthenium, tantalum, zirconium, hafnium, yttrium, nickel, manganese, iron, It may be mixed with copper, silver, gold, gadolinium, and combinations thereof. In one or more embodiments, the high surface area refractory metal oxide includes any high surface area refractory metal oxide known in the art. For example, high surface area refractory metal oxides include alumina, zirconia, alumina-zirconia, lanthana-alumina, lantana-zirconia-alumina, baria-alumina, baria-lantana-alumina, baria-lantana-neodymia-alumina. , alumina-chromia, ceria, and alumina-ceria. In one or more embodiments, the rare earth oxide-high surface area refractory metal oxide particles comprise ceria-alumina particles. In a specific embodiment, the ceria-alumina particles are in the range of from about 20% to about 80% on an oxide basis by weight percent in the first layer, for example 20%, 25%, 30%, 35%, 40%, 45 %, 50%, 55%, 60%, 65%, 70%, 75%, or 80% ceria phase present. In one or more specific embodiments, the average CeO ₂ crystallite size of fresh and aged samples obtained from XRD can be used as a measure of CeO ₂ hydrothermal stability. Thus, in one or more embodiments, CeO ₂ is hydrothermal stability and is in the form of crystallites having an average crystallite size of less than 130 Å after aging at 950° C. for 5 hours in 2% O ₂ and 10% water vapor in N ₂ . do. In a specific embodiment, the ceria-alumina particles comprise a ceria phase present in an amount of about 50% on an oxide basis by weight percent of the composite. In another specific embodiment, the ceria-alumina particles comprise a ceria phase present in an amount of about 30% on an oxide basis by weight percent of the composite.

In one or more embodiments, CeO ₂ is in the form of crystallites that are hydrothermal stability and resistant to growth into larger crystallites upon aging at 950°C. As used herein, the term “resistant to growth” means that crystallites grow to an average size of 130 Angstroms or less with aging. In a specific embodiment, the CeO ₂ crystallite size, as determined by XRD, is less than 130 Å after aging the catalytic article at 950° C. for 5 hours in 2% O ₂ and 10% water vapor/N ₂ . According to one or more embodiments, the CeO ₂ crystallite size of the powder sample and the coated catalyst are different. In the coated catalyst, other washcoat components may have a stabilizing effect on CeO ₂ . Thus, after the same 950° C. aging, the CeO ₂ crystallite size of the coated catalyst is smaller than that of the powder.

As used herein, the term “average crystallite size” refers to the average size determined by XRD as described below.

As used herein, the term “XRD” refers to x-ray diffraction crystallization, a method for determining the atomic and molecular structure of a crystal. In XRD, crystalline atoms diffract an x-ray beam in a number of specific directions. By measuring the angle and intensity of the diffracted beam, a three-dimensional image of the electron density in the crystal can be generated. From this electron density, the positions of atoms in the crystal, as well as their chemical bonds, disorder, and other information can be determined. In particular, XRD can be used to estimate the crystallite size; The peak width is inversely proportional to the crystallite size; The smaller the crystallite size, the wider the peak. In one or more embodiments, XRD is used to determine the average crystallite size of CeO ₂ particles.

The width of the XRD peak is interpreted as a combination of width broadening effects related to both size and strain. Equations used to determine both are provided below. The first equation below is the Scherrer equation used to convert the full width at half maximum, ie, the FWHM information, to the crystallite size for a given phase. The second equation is used to calculate the strain in the crystal from the peak width information, and the total width or width of the peak is considered to be the sum of these two effects as shown in the third equation. It should be noted that the magnitude and strain width extension vary in different ways with respect to the Bragg angle θ. The constants of Scherrer's equation are discussed below.

The constants in Scherrer's equation are:

K: shape constant, use a value of 0.9

L: peak width, corrected for contributions from optics through the use of the NIST SRM 660b LaB6 Line Position & Line Shape Standard

Θ: ½ of the 2θ value of the reflection of interest

λ: wavelength of radiation 1.5406 Å

The crystallite size is understood to be the length of the coherent scattering domain in the direction perpendicular to the set of lattice planes causing the reflection. In the case of CeO ₂ , the CeO ₂ 111 reflection is the maximum intensity peak in the X-ray diffraction pattern of CeO ₂ . The CeO ₂ (111) plane of the atom intersects each of the associated crystal axes and is perpendicular to the solid diagonal represented by the <111> vector. Therefore, a crystallite size of 312 Å calculated from the FWHM of the CeO ₂ 111 reflection would be considered to be approximately 100 layers of the (111) plane of the atom.

Different directions in the crystal, and thus reflections, will result in similar, but different crystallite size values. This value will be correct only if the crystal is perfectly spherical. Using the Williamson Hall plot, the magnitude and strain effects are interpreted by considering the total peak width as the following linear equation where the slope of the line represents the strain and the intercept is the size of the crystal.

To determine the crystallite size of a material, the FWHM value of a single reflection or from a complete X-ray diffraction pattern needs to be determined. Traditionally, a single reflection is fitted to determine the FWHM value of that reflection, the FWHM value is corrected for contributions from the instrument, and then the corrected FWHM value is converted to a determinant size value using Scherrer's equation. This will be done by ignoring any effect from strain in the crystal. This method was mainly used for questions regarding the crystallite size of noble metals with only useful single reflections. It should be noted that in fitting the peaks it is desirable to have a clean reflection that is not superimposed by reflections from other phases. Since this is a rare case in the washcoat formulation of the present invention, it was changed to using the Rietveld method. The Rietveld method allows fitting of complex X-ray diffraction patterns using known crystal structures of the phases present. The crystal structure acts as a limit or brake on the fitting method. Phase content, lattice parameters, and FWHM information are varied for each phase until the overall model matches the experimental data.

In the following examples, experimental patterns of new and aging samples were fitted using the Rietveld method. The crystallite size was determined using the FWHM curves determined for each phase in each sample. Strain effects were excluded.

As used herein, the term "alkaline earth metal" refers to one defined in the Periodic Table of the Elements, including beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). more than one chemical element. In one or more embodiments, the first layer comprises an alkaline earth metal. In one or more embodiments, the alkaline earth metals in the first layer may include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). In a specific embodiment, the alkaline earth metal in the first layer comprises barium. The alkaline earth metal may be present in the first layer in an amount ranging from about 5% to 30% by weight on an oxide basis, based on the weight of the first layer. In a specific embodiment, the alkaline earth metal in the first layer comprises barium, which is present in an amount ranging from about 5% to about 30% by weight on an oxide basis. In one or more embodiments, the alkaline earth metal may be incorporated into the layer as a salt (eg, BaCO ₃ ).

In one or more embodiments, without wishing to be bound by theory, the additional ceria surface area resulting from the smaller crystallite size is greater BaCO ₃ based NO _x trapping due to superior BaCO ₃ dispersion, higher CeO ₂ based NO _x at low temperature. It is thought to allow for trapping, improved NO _x reduction due to more efficient WGS, and improved NO oxidation and NO _x reduction due to good PGM dispersion. Thus, the incorporation of barium (BaCO ₃ ) into ceria-alumina (CeO ₂ /Al ₂ O ₃ ) has a tremendous stabilizing effect on CeO ₂ , improved hydrothermal stability over traditional LNT technology, higher NO _x trapping ability. , and an LNT catalyst material in the first layer having a higher NO _x conversion.

In one or more embodiments, the composite of CeO ₂ and Al ₂ O ₃ in the first layer contains ceria in the range of 20 to 80% by weight on an oxide basis, for example 20%, 25%, 30%, 35%, 40 %, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%.

As used herein, the term "platinum group metal" or "PGM" refers to one or more chemical elements as defined in the Periodic Table of the Elements, including platinum (Pt), palladium, rhodium, osmium, iridium, and ruthenium, and mixtures thereof. In one or more embodiments, the first layer comprises at least one first platinum group metal supported on rare earth oxide-high surface area refractory metal oxide particles (eg, ceria-alumina). In one or more embodiments, the first platinum group metal is selected from the group consisting of platinum, palladium, rhodium, and mixtures thereof. In a specific embodiment, the first platinum group metal component comprises both palladium and platinum. In another embodiment, the first platinum group metal comprises only platinum. In a very specific embodiment, the first layer comprises Pt/Pd supported on BaCO ₃ /(CeO ₂ —Al ₂ O ₃ ) particles. In another specific embodiment, the first layer comprises Pt supported on BaCO ₃ /(CeO ₂ —Al ₂ O ₃ ) particles.

In general, there are no specific limitations as far as the weight ratio of platinum to palladium of the first layer is concerned. In general, there is no specific limitation as far as the palladium content of the first layer is concerned. In addition, there is no specific limitation as far as the platinum content of the first layer is concerned.

In general, there is no specific limitation as far as the total platinum group metal content of the layered catalyst composite is concerned. In one or more embodiments, the first layer comprises platinum and palladium and the second layer comprises palladium and rhodium. In general, there is no specific limitation as far as the total platinum group metal content of the layered catalyst composite is concerned.

In one or more embodiments, the second layer comprises a first oxygen storage component (OSC) and/or a second platinum group metal component supported on a first refractory metal oxide support, and, optionally, a second refractory metal oxide support or a second oxygen. and a third platinum group metal supported on the storage component. In one or more embodiments, the second platinum group metal component is selected from platinum, palladium, rhodium, or mixtures thereof. In a specific embodiment, the second platinum group metal component comprises palladium. In general, there is no specific limitation as far as the palladium content of the second layer is concerned.

In one or more embodiments, the second layer is free of a third platinum group metal. In one or more embodiments, when present, the third platinum group metal is selected from platinum, palladium, rhodium, and mixtures thereof. In a specific embodiment, the third platinum group metal component comprises rhodium. In general, there is no specific limitation as far as the rhodium content of the second layer is concerned.

In one or more embodiments, the first layer comprises barium in an amount ranging from about 5% to 30% by weight of the first layer on an oxide basis. In a specific embodiment, the first layer comprises Pt/Pd supported on BaCO ₃ /(CeO ₂ —Al ₂ O ₃ ) particles.

As used herein, the term "oxygen storage component" (OSC) has a polyvalent state and is capable of reacting actively with a reducing agent such as carbon monoxide (CO) or hydrogen under reducing conditions and then reacting with an oxidizing agent such as oxygen or nitrous oxide under oxidizing conditions. object that can Examples of suitable oxygen storage components include rare earth oxides, particularly ceria. The OSC may also include, in addition to ceria, one or more of lanthana, praseodymia, neodymia, niobia, europia, samaria, ytterbia, yttria, zirconia, and mixtures thereof. The rare earth oxide may be in bulk (eg, particulate) form. The oxygen storage component may include cerium oxide (ceria, CeO ₂ ) in a form exhibiting oxygen storage properties. The lattice oxygen of ceria can react with carbon monoxide, hydrogen, or hydrocarbons under rich A/F conditions. Upon lean exposure, the reduced ceria has the ability to recapture oxygen from air and/or NO _x species, thus accelerating the conversion of NO _x .

In one or more embodiments, the first and second oxygen storage components comprise a ceria-zirconia complex or a rare earth-stabilized ceria-zirconia. In a specific embodiment, the first oxygen storage component and the second oxygen storage component comprise different ceria-zirconia composites. Specifically, the first oxygen storage component comprises in the range of 35 to 45 weight percent ceria and 43 to 53 weight percent zirconia, and the second oxygen storage component comprises in the range 15 to 25 weight percent ceria and 70 to 80 weight percent. range of zirconia.

According to one or more embodiments, the layered catalyst composites of the present invention are free of hydrocarbon trapping materials. As used herein, the term “free of hydrocarbon trapping material” means that there is no intentionally added hydrocarbon trapping material to the layered catalyst composite. As used herein, the term "hydrocarbon trapping material" refers to a material having the ability to reversibly trap hydrocarbons, particularly hydrocarbon emissions generated during cold start periods. In one or more embodiments, the layered catalyst composite contains less than 1% hydrocarbon trapping material.

Typically, the layered catalyst composite of the present invention is disposed on a substrate. The substrate may be any of the materials typically used in the manufacture of catalysts and will typically comprise a ceramic or metallic honeycomb structure. Any suitable substrate, such as a monolithic substrate of the type (referred to herein as a flow-through substrate) having fine, parallel gas flow passages extending therethrough from an inlet or outlet face of the substrate, such that the passageways are open to fluid flow therethrough. ) can be used. A passage, which is an essentially straight path from the fluid inlet to the fluid outlet, is defined by a wall, the wall coated with the catalytic material as a washcoat so that the gas flowing through the passage contacts the catalytic material. The flow passages of the monolithic substrate are thin walled channels, which can have any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, and the like.

Such monolithic substrates may contain up to about 900 or more flow passages (or "cells") per square inch of cross-section, although even fewer may be used. For example, the substrate may have from about 7 to 600 cells per square inch, more typically from about 100 to 400 cells per square inch (“cpsi”). A cell may have a cross-section that is rectangular, square, circular, oval, triangular, hexagonal, or other polygonal shape. The ceramic substrate may be made of any suitable refractory material, such as cordierite, cordierite-alumina, silicon nitride, or silicon carbide, or the substrate may be composed of one or more metals or metal alloys.

The layered catalyst composite according to an embodiment of the present invention may be applied to the substrate surface by any means known in the art. For example, the catalyst washcoat can be applied by spray coating, powder coating, or brushing or by dipping the surface into the catalyst composition.

In one or more embodiments, the layered catalyst composite is disposed on a honeycomb substrate.

The washcoat composition of the present invention can be seen more easily with reference to FIGS. 1 and 2 . 1 and 2 show a refractory substrate member 2 according to one embodiment of the present invention. Referring to FIG. 1 , the refractory substrate member 2 has a cylindrical shape having a cylindrical outer surface 4 , an upstream end face 6 and a downstream end face 8 identical to the end face 6 . The base member 2 has a plurality of fine, parallel gas flow passages 10 formed therein. As shown in FIG. 2 , a flow passage 10 is defined by a wall 12 and extends through the substrate from an upstream end face 6 to a downstream end face 8 , the passage 10 including a fluid, e.g. For example, the gas stream is not obstructed to allow longitudinal flow through the substrate by the gas flow passage 10 . A separate bottom layer 14 , sometimes referred to in the art and hereinafter as a “washcoat”, is adhered or coated onto the wall 12 of the substrate member. As shown in FIG. 2 , a second, separate top washcoat layer 16 is coated over the bottom washcoat layer 14 . In one or more embodiments, the first layer becomes the bottom washcoat layer 14 and the second layer becomes the top washcoat layer 16 . In another embodiment, the second layer becomes the bottom washcoat layer 14 and the first layer becomes the top washcoat layer 16 .

As shown in FIG. 2 , the substrate member includes void spaces provided by gas flow passages 10 , and the cross-sectional area of these passages 10 and the thickness of the walls 12 defining the passageways depend on the type of substrate member. each will be different. Likewise, the weight of the washcoat applied to such a substrate will vary from case to case. Therefore, when describing the amount of the catalytic metal component or other component of a washcoat or composition, it is convenient to use units of the weight of the component per unit volume of the substrate. Accordingly, herein, the weight of the component per volume of a substrate member, wherein the units of grams per cubic inch (“g/in ³ ”) and grams per cubic foot (“g/ft ³ ”) include the volume of void space of the substrate member. used to mean

During operation, exhaust gas emissions from a lean burn engine, including hydrocarbons, carbon monoxide, nitrogen oxides, and sulfur oxides, first encounter the top washcoat layer 16 and then the bottom washcoat layer 14 .

In one embodiment, the layered catalyst composite of the present invention is coated on a single substrate or substrate member, with one layer (eg, second layer) on top of another layer (eg, first layer). It contains two distinct layers. In this embodiment, the first layer is coated over the entire axial length of the substrate (eg, the flow-through monolith) and the second layer is coated over the entire axial length of the first layer.

In one or more embodiments, the improved NO _x conversion when subjected to high temperature harsh aging allows the layered catalyst composite according to one or more embodiments to be placed in a close-coupled position, which increases with increasing temperature. It is beneficial to reduce system N ₂ O emissions as ₂ O formation is reduced.

According to one or more embodiments, the layered catalyst composite is effective to provide both lean NO _x trap (LNT) functionality and three-way conversion (TWC) functionality. As used herein, the term “conversion” encompasses both chemical conversion of the effluent to other compounds, as well as trapping of the effluent by chemical and/or adsorbent bonding with a suitable trapping material. As used herein, the term “emissions” refers to exhaust gas emissions, more specifically exhaust gas emissions comprising NO _x , CO, and hydrocarbons.

In a specific embodiment, the substrate comprises a flow-through carrier, the first layer is disposed on the substrate, and the second layer is disposed on the top surface of the first layer. The first layer comprises ceria-alumina particles having a ceria phase present in the range of from about 20% to about 80% on an oxide basis by weight percent in the composite, the ceria-alumina particles comprising barium supported on the particles, and It has platinum and palladium supported on it. The second layer comprises Pd supported on a ceria-zirconia composite and Rh supported on alumina.

Catalytic converters must effectively convert hydrocarbons at low temperatures during lean operation. This also applies to hydrocarbons (HC) and nitrogen oxides (NO _x ) under conditions favorable to stoichiometric exhaust gases that may occur during operation, as well as in the cold start-up phase. A further challenge is to store nitrogen oxides during lean burn and reduce these oxides during rich burn. In order to utilize lean burn as much as possible, NO _x storage should be possible over a wide temperature range.

Thus, the layered catalyst composite of the present invention is effective in providing both lean NO _x trap functionality (LNT) and three-way conversion (TWC) functionality. In one or more embodiments, the layered catalyst composites of the present invention are effective to simultaneously store NO _x and also oxidize CO, HC, and NO to NO ₂ . According to one or more embodiments, the layered catalyst composite under rich conditions is effective at simultaneously converting CO and HC and also releasing and reducing NO _x , and under stoichiometric conditions the layered catalyst composite simultaneously converting CO, HC, and NO _x effective to do

Sometimes particulates are present in the exhaust gas stream and the layered catalyst composite can also provide the ability to oxidize any particulates.

The layered catalyst composite of the present invention may be used in an integrated emission treatment system comprising one or more additional components for treatment of exhaust gas emissions. Accordingly, a second aspect of the present invention relates to an exhaust gas treatment system. In one or more embodiments, an exhaust gas treatment system comprises an engine and a layered catalyst composite of the present invention. In a specific embodiment, the engine is a lean burn engine. In another specific embodiment, the engine is a lean gasoline direct injection engine. In one or more embodiments, the exhaust gas treatment system comprises a lean burn engine upstream from the layered catalyst composite of one or more embodiments. The exhaust gas treatment system may further include a catalyst, and optionally a particulate filter. In one or more embodiments, the catalyst is selected from the group consisting of TWC, SCR, GPF, LNT, AMOx, SCR on a filter, and combinations thereof. The layered catalyst composite may be located upstream or downstream of the catalyst. In one or more embodiments, the catalyst is an SCR catalyst located downstream of the bed catalyst composite. In one or more embodiments, the particulate filter may be selected from a gasoline particulate filter, a soot filter, or an SCR on filter. Particulate filters may be catalyzed for specific functions. The layered catalyst composite may be located upstream or downstream of the particulate filter.

In a specific embodiment, the particulate filter is a catalyzed soot filter (CSF). The CSF may comprise a substrate coated with a washcoat layer containing one or more catalysts for combustion of trapped soot and/or oxidation of exhaust gas stream emissions. In general, the soot combustion catalyst may be any known catalyst for the combustion of soot. For example, CSF may be an oxidation catalyst for the combustion of one or more high surface area refractory oxides (e.g., alumina, silica, silica alumina, zirconia, and zirconia alumina) and/or unburned hydrocarbons and to some extent particulate matter (e.g., for example, ceria-zirconia). In one or more embodiments, the soot combustion catalyst is an oxidation catalyst comprising one or more noble metal (PM) catalysts (platinum, palladium, and/or rhodium).

In general, any filter substrate known in the art can be used, including, for example, honeycomb wall-flow filters, wound or packed fiber filters, open cell foams, sintered metal filters, and the like, and wall-flow filters is specifically exemplified. Wall-flow substrates useful for supporting CSF compositions have a plurality of fine, substantially parallel gas flow passages extending along a longitudinal axis of the substrate. Typically, each passage is blocked at one end of the substrate body, and its alternating passage is blocked at the opposite end face. Such monolithic substrates may contain up to about 900 or more flow passages (or "cells") per square inch of cross-section, although even fewer may be used. For example, the substrate may have from about 7 to 600 cells per square inch, more typically from about 100 to 400 cells per square inch (“cpsi”). The porous wall-flow filter used in embodiments of the present invention is optionally catalyzed in that the walls of the element have on or contain one or more catalytic materials thereon, such CSF catalyst compositions are described above. . The catalytic material may be present only on the inlet side of the element wall, only on the outlet side, on both the inlet and outlet, or the wall itself may consist entirely or partially of the catalytic material. In another embodiment, the present invention may include the use of a combination of one or more washcoat layers of catalytic material and one or more washcoat layers of catalytic material on the inlet and/or outlet walls of an element.

A third aspect of the present invention relates to a method of treating a gas comprising hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ). In one or more embodiments, the method comprises contacting a gas with a layered catalyst composite of the present invention. In a specific embodiment, the layered catalyst composite under lean conditions is effective at simultaneously storing NO _x and also oxidizing CO, HC, and NO; Under abundant conditions, the layered catalyst complex is effective in simultaneously converting CO and HC and also releasing and reducing NO _x ; Under stoichiometric conditions, the layered catalyst complex is effective in simultaneously converting CO, HC, and NO _x .

A further aspect of the present invention relates to a method for preparing a layered catalyst composite. In one or more embodiments, the method comprises providing a carrier and coating the carrier with first and second layers of a catalytic material. In a specific embodiment, the first layer comprises at least one agent supported on rare earth oxide-high refractory metal oxide particles, alkaline earth metal supported on rare earth oxide-high refractory metal oxide particles, and rare earth oxide-high refractory metal oxide particles. 1 Contains a platinum group metal component. The second layer, the outermost layer of the composite, is supported on a first oxygen storage component (OSC) or a second platinum group metal component supported on a first refractory metal oxide support and a second refractory metal oxide support or a second oxygen storage component. and a third platinum group metal component.

The present invention is now described with reference to the following examples. Before describing some exemplary embodiments of the present invention, it is to be understood that the present invention is not limited to the details of construction or process steps detailed in the description that follows. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

Example

Example One - LNT - TWC Preparation of catalyst

To demonstrate the advantages of the present invention, examples of LNT-TWC catalysts were prepared. This two-layer formulation, comprising an undercoat washcoat layer and a top washcoat layer, is coated on a flowable ceramic monolith based carrier having a cell density of 400 cells per square inch (cpsi) and a wall thickness of 4 mils; , the top washcoat layer was coated over the undercoat washcoat layer. The catalyst had a nominal PGM loading of 185 g/ft ³ in total, and the Pt/Pd/Rh ratio was 63/117/5.

undercoat washcoat layer

CeO ₂ -Al ₂ O 3 containing 50% by weight CeO ₂ and 50% by weight Al ₂ O ₃ by weight, such that the BaCO ₃ /(CeO ₂ -Al ₂ O ₃ ) composite has a BaCO ₃ content of about 26% by weight _. The particles were impregnated with barium acetate solution. The mixture was dried at 110° C. and calcined at 720° C. for 2 hours. Pd in the form of palladium nitrate and Pt in the form of a platinum amine solution were introduced onto the support material BaCO ₃ /(CeO ₂ —Al ₂ O ₃ ) by conventional incipient wetness impregnation. Magnesium acetate to provide about 87 wt % BaCO ₃ /(CeO ₂ —Al ₂ O ₃ ), 1 wt % Pt, 0.1 wt % Pd, 7 wt % MgO, 4 wt % ZrO ₂ A slurry mixture containing zirconium acetate was coated onto a ceramic honeycomb substrate. After calcination at 550° C. for 1 hour in air, the total washcoat loading of the undercoat layer was about 3.4 g/in ³ .

top coat layer

The top layer was placed over the undercoat layer. Pd in the form of palladium nitrate was introduced onto the OSC material and Rh in the form of rhodium nitrate was introduced onto the activated γ-alumina. Barium acetate to provide about 15% by weight of active γ-alumina, 76% by weight of an OSC material with accelerator (CeO ₂ /ZrO ₂ ), 2% by weight Pd, 0.1% by weight Rh, 5% by weight BaCO ₃ , a slurry mixture containing zirconium acetate providing 2 wt % ZrO ₂ was coated over the entire undercoat layer. The total washcoat of the top layer after 550° C. calcination was about 3.0 g/in ³ .

Example 2 - LNT - TWC Preparation of catalyst

To demonstrate the advantages of the present invention, examples of LNT-TWC catalysts were prepared. This two-layer formulation, comprising an undercoat washcoat layer and a top washcoat layer, is coated on a flowable ceramic monolith based carrier having a cell density of 400 cells per square inch (cpsi) and a wall thickness of 4 mils; , the top washcoat layer was coated over the undercoat washcoat layer. The catalyst had a nominal PGM loading of 185 g/ft ³ in total, and the Pt/Pd/Rh ratio was 63/117/5.

undercoat washcoat layer

CeO ₂ -Al ₂ O ₃ containing 30 wt% CeO ₂ and 70 wt% Al ₂ O ₃ so that the BaCO ₃ /(CeO ₂ -Al ₂ O ₃ ) composite has a BaCO ₃ content of about 13 wt% The particles were impregnated with barium acetate solution. The mixture was dried at 110° C. and calcined at 720° C. for 2 hours. Pd in the form of palladium nitrate and Pt in the form of a platinum amine solution were introduced onto the support material BaCO ₃ /(CeO ₂ —Al ₂ O ₃ ) by a conventional initial wet impregnation method. Magnesium acetate to provide about 87 wt % BaCO ₃ /(CeO ₂ —Al ₂ O ₃ ), 1 wt % Pt, 0.1 wt % Pd, 7 wt % MgO, 4 wt % ZrO ₂ A slurry mixture containing zirconium acetate was coated onto a ceramic honeycomb substrate. After calcination at 550° C. for 1 hour in air, the total washcoat loading of the undercoat layer was about 3.4 g/in ³ .

top coat layer

The top layer was placed over the undercoat layer. Pd in the form of palladium nitrate was introduced onto the OSC material and Rh in the form of rhodium nitrate was introduced onto the activated γ-alumina. Barium acetate to provide about 18 wt % active γ-alumina, 70 wt % OSC material with accelerator (CeO ₂ /ZrO ₂ ), 2.7 wt % Pd, 0.1 wt % Rh, 8.6 wt % BaCO ₃ , a slurry mixture containing zirconium acetate providing 2 wt % ZrO ₂ was coated over the entire undercoat layer. The total washcoat of the top layer after 550°C calcination was about 2.4 g/in ³ .

Example 3 - LNT Preparation of catalyst (for comparison)

To demonstrate the advantages of the present invention, comparative examples of state-of-the-art LNT catalysts were prepared. This two-layer formulation, comprising an undercoat washcoat layer and a top washcoat layer, is coated on a flowable ceramic monolith based carrier having a cell density of 400 cells per square inch (cpsi) and a wall thickness of 4 mils; , the top washcoat layer was coated over the undercoat washcoat layer. The catalyst has a nominal PGM loading of 120 g/ft ³ in total, with a Pt/Pd/Rh ratio of 103/12/5, which has a nominal PGM loading of 185 g/ft ³ and a Pt/Pd/Rh ratio of 63 Cost equivalent to Examples 1, 2, and 7 of /117/5.

The undercoat layer contains active γ-alumina, cerium oxide, barium carbonate, magnesia, zirconia, platinum, and palladium, respectively, by approximately 38%, 41%, 14%, 6%, 2%, by calcined weight of the catalyst; concentrations of 0.7% and 0.09%. Pd in the form of palladium nitrate and Pt in the form of a platinum amine solution were introduced onto the support material by conventional initial wet techniques. After calcination at 550° C. for 1 hour in air, the total washcoat loading of the undercoat layer was about 5.3 g/in ³ .

The topcoat layer, disposed on the undercoat layer, contains active γ-alumina, cerium oxide, platinum, palladium and rhodium, respectively, by approximately 57%, 41%, 2%, 0.2 and 0.2% by calcined weight of the catalyst. was contained at a concentration of Pt in the form of a platinum amine solution and Pd in the form of a palladium nitrate solution were introduced into the γ-alumina phase, and Rh in the form of rhodium nitrate was introduced into the ceria phase by a conventional initial wet technique. The topcoat layer was coated over the entire undercoat layer. The total washcoat of the topcoat layer after 550°C calcination was about 1.23 g/in ³ .

Example 4 - TWC Preparation of catalyst (for comparison)

To demonstrate the advantages of the present invention, comparative examples of state-of-the-art TWC catalysts were prepared. This single layer formulation was coated on a flowable ceramic monolith based carrier having a cell density of 400 cells per square inch (cpsi) and a wall thickness of 4 mils. The catalyst has a nominal PGM loading of 248 g/ft ³ in total, a Pt/Pd/Rh ratio of 24/220/4, which has a nominal PGM loading of 185 g/ft ³ and a Pt/Pd/Rh ratio of 63 Cost equivalent to Examples 1, 2, and 7 of /117/5.

The catalyst washcoat contains active γ-alumina, OSC material with promoter (CeO ₂ /ZrO ₂ ), barium carbonate, zirconia, platinum, palladium and rhodium, each containing approximately 36%, 56%, by calcined weight of the catalyst, Concentrations of 4%, 1%, 0.3%, 3% and 0.06% were contained. After calcination at 550° C. for 1 hour in air, the total washcoat loading was about 4.0 g/in ³ .

Example 5 - Circulation NO _x Conversion rate and NO _x trapping ability test

The NO _x trapping and reducing actions of Examples 1, 2, and 3 were evaluated as fresh and after aging at 950° C. for 5 hours in 2% O ₂ and 10% water vapor in N ₂ . Catalysts were evaluated in a reactor test rig equipped with FTIR analysis equipment. The evaluation was performed in 10 cycles comprising 120 seconds of lean gas exposure and 5 seconds of rich gas exposure. Purging with a gas mixture of CO ₂ , H ₂ O and N ₂ was performed between lean gas exposure and rich gas exposure for evaluation at 200, 250, 300, 350, and 400° C. 10, 10, and 6 respectively. , 4, and 4 seconds were applied. After the lean/rich cycle, the catalyst was regenerated in the rich gas for 1 minute and then exposed to the lean gas. The feed gas composition and space velocity at each test temperature are listed in Table 1.

<Table 1>

The NO _x trapping ability of the catalyst was measured after one minute of rich exposure and expressed as the amount of NO _x removed from the feed gas when 100 ppm of NO _x was released. Cyclic NO _x conversion of the catalyst was determined as the average NO _x conversion of the last 5 lean/rich cycles.

Example 6 - XRD measurement

The CeO ₂ crystallite size of the aging samples of Examples 1 and 3 was measured by XRD. Samples were ground using a mortar and then filled onto low background slides for analysis. Data were collected in Bragg-Brentano geometry using a PANalytical MPD X'Pert Pro diffraction system. Cu _Kα radiation was used in the analysis with generator settings of 45 kV and 40 mA. Optical paths are 1/4° divergence slit, 0.04 radian soller slit, 15 mm mask, 1/2° anti-scatter slit, 1/4° anti-scatter It consisted of a slit, a Ni filter, and an X'Celerator linear position-sensitive detector. Data were collected from 10° to 90°2θ using a step size of 0.026°2θ and a count time of 600 seconds per step. For phase identification, Jade Plus 9 analytical X-ray diffraction software was used. The phases present were identified by search/matching of the PDF-4/Full File database of the International Center for Diffraction Data (ICDD). All numerical values were determined using the Rietveld method.

As shown in Figures 3a and 3b, LNT-TWC catalyst Examples 1 and 2 significantly improved cyclic NO _x conversion and NO _x trapping ability compared to TWC catalyst Comparative Example 4. Although the cyclic NO _x conversion and NO _x trapping capacity of Examples 1 and 2 in fresh condition are not as high as the LNT catalyst of Example 3 in fresh condition, Examples 1 and 2 exhibit higher hydrothermal stability than Example 3. had As shown in FIGS. 4A and 4B , after aging at 950° C. for 5 hours in 2% O ₂ and 10% water vapor in N ₂ , Examples 1 and 2 had higher cyclic NO _x conversion and NO _x trapping than Example 3 showed ability.

The high hydrothermal stability of Example 1 was also demonstrated by the average CeO ₂ crystallite size measured by XRD after aging at 950° C. for 5 hours in 2% O ₂ in N ₂ and 10% water vapor. The results are presented in Table 2. CeO ₂ present in Example 1 had a higher hydrothermal stability than that of Example 3. The average CeO ₂ crystallite size of Example 1 after aging in 2% O ₂ in N ₂ and 10% water vapor at 950° C. for 5 hours was 109 Å. The average CeO ₂ crystallite size of Example 3 after aging in 2% O ₂ in N ₂ and 10% water vapor at 950° C. for 5 hours was 197 Å. This stabilizing effect would be beneficial for NO _x trapping and NO _x reducing action. The additional ceria surface area resulting from the smaller crystallite size will allow for more ceria-based NO _x trapping at lower temperatures, improve WGS, and improve PGM dispersion.

<Table 2>

*Measured after aging at 950° C. for 5 hours in 2% O ₂ in N ₂ and 10% water vapor

Using the Rietveld method, the experimental patterns of the aged Examples 1 and 3 were fitted. The crystallite size was determined using the FWHM curves determined for each phase in each sample. Strain effects were excluded.

Examples 1 and 4 were each applied to treating the exhaust gas stream of a lean burn gasoline engine after aging at 950° C. for 64 hours in an internal combustion engine located downstream of the TWC catalyst. As shown in Figures 5a and 5b, in the FTP75 test cycle, Example 1, when positioned downstream of the TWC catalyst, significantly reduced NO _x emissions compared to Example 4 when positioned downstream of the same TWC catalyst. , Example 1 showed equivalent non-methane hydrocarbon (NMHC) emissions to Example 4.

As shown in FIG. 6 , TEM of the undercoat layer of Example 1 showed that the plates of Al ₂ O ₃ and the round aggregates of CeO ₂ were intimately mixed, and the nano-sized platinum particles were mixed with CeO ₂ and Al ₂ O _{3 .} It was shown to be located on the particle.

As shown in FIG. 7 , TEM of the topcoat layer of Example 1 showed that Rh particles were located on Al ₂ O ₃ and Pd particles were located on the OSC material.

Example 7

To demonstrate the advantages of the present invention, examples of LNT-TWC catalysts were prepared. This two-layer formulation, comprising an undercoat washcoat layer and a top washcoat layer, is coated on a flowable ceramic monolith based carrier having a cell density of 400 cells per square inch (cpsi) and a wall thickness of 4 mils; , the top washcoat layer was coated over the undercoat washcoat layer. The catalyst had a nominal PGM loading of 185 g/ft ³ in total, and the Pt/Pd/Rh ratio was 63/117/5.

undercoat washcoat layer

Pd in the form of palladium nitrate was introduced onto the OSC material and Rh in the form of rhodium nitrate was introduced onto the activated γ-alumina. Zirconium acetate to provide about 15 wt % active γ-alumina, 80 wt % OSC material with accelerator (CeO ₂ /ZrO ₂ ), 2.3 wt % Pd, 0.1 wt % Rh, 2 wt % ZrO ₂ was coated on a ceramic honeycomb substrate. The total washcoat of the top layer after 550° C. calcination was about 2.8 g/in ³ .

top coat layer

The top layer was placed over the undercoat layer. CeO ₂ -Al ₂ O 3 containing 50% by weight CeO ₂ and 50% by weight Al ₂ O ₃ by weight, such that the BaCO ₃ /(CeO ₂ -Al ₂ O ₃ ) composite has a BaCO ₃ content of about 26% by weight _. The particles were impregnated with barium acetate solution. The mixture was dried at 110° C. and calcined at 720° C. for 2 hours. Pd in the form of palladium nitrate and Pt in the form of a platinum amine solution were introduced onto the support material BaCO ₃ /(CeO ₂ —Al ₂ O ₃ ) by a conventional initial wet impregnation method. Magnesium acetate to provide about 87 wt % BaCO ₃ /(CeO ₂ —Al ₂ O ₃ ), 1 wt % Pt, 0.1 wt % Pd, 7 wt % MgO, 4 wt % ZrO ₂ A slurry mixture containing zirconium acetate was coated over the entire undercoat layer. After calcination at 550° C. for 1 hour in air, the total washcoat loading of the undercoat layer was about 3.4 g/in ³ .

Claims (15)

a catalytic material on a substrate, wherein the catalytic material comprises at least two layers, wherein
The first layer comprises rare earth oxide-high surface area refractory metal oxide particles exhibiting a BET surface area greater than 60 square meters per gram, an alkaline earth metal supported on the rare earth oxide-high surface area refractory metal oxide particles, and the rare earth oxide-high surface area refractory metal oxide particles. at least one first platinum group metal component supported on oxide particles;
The second layer comprises a first oxygen storage component (OSC) and/or a second platinum group metal component supported on the first refractory metal oxide support, and a third supported on the second refractory metal oxide support or second oxygen storage component. a platinum group metal;
wherein the rare earth oxide-high surface area refractory metal oxide particles comprise ceria-alumina particles having a ceria phase present in the range of 30% to 50% oxide based on weight percent of the particles;
the alkaline earth metal comprises barium in an amount ranging from 5% to 30% by weight of the first layer on an oxide basis;
the first platinum group metal component comprises palladium and platinum;
the second platinum group metal component comprises palladium;
the third platinum group metal component comprises rhodium;
the first and second oxygen storage components comprise a ceria-zirconia complex or a rare earth-stabilized ceria-zirconia;
the first and second refractory metal oxide supports comprise alumina;
wherein the first layer is disposed on a substrate comprising the flow-through monolith and the second layer is disposed on the first layer;
A layered catalyst composite for the exhaust stream of an internal combustion engine. The method of claim 1 , wherein the first oxygen storage component and the second oxygen storage component comprise different ceria-zirconia composites, and wherein the first oxygen storage component is in the range of 35 to 45 weight percent ceria and 43 to 53 weight percent zirconia. wherein the second oxygen storage component comprises ceria in the range of 15 to 25 wt% and zirconia in the range of 70 to 80 wt%. The layered catalyst composite of claim 1 , wherein the second layer further comprises a second alkaline earth metal supported on the first refractory metal oxide support. An exhaust gas treatment system comprising the layered catalyst composite of any one of claims 1 to 3, located downstream of an engine. A method comprising contacting a gas with the layered catalyst composite of any one of claims 1 to 3, wherein
Under lean conditions, the layered catalyst composite is effective in simultaneously storing NO _x and also oxidizing CO, HC, and NO;
Under abundant conditions, the layered catalyst complex is effective in simultaneously converting CO and HC and also releasing and reducing NO _x ;
Under stoichiometric conditions, the layered catalyst composite is effective at simultaneously converting CO, HC, and NO _x ,
A method of treating gases comprising hydrocarbons, carbon monoxide, and nitrogen oxides. delete delete delete delete delete delete delete delete delete delete

Images